feat(bot): add a custom changeset bot (#2)

* feat(bot): add a custom changeset bot

* chore(bot): update human-id import

* chore: add test changeset

* chore(bot): update comment to only show info about 1 package

* chore(bot): update wording in comment

* chore: move bot into main pnpm workspace, add to tsconfig

* chore(bot): update emoji

* chore(bot): update comment links

* chore(bot): use a bullet point instaed of a dash between links

* docs(changesets): add a guide for changesets

Author: ryanclark

.changeset/khaki-kids-juggle.md

@@ -0,0 +1,5 @@
+---
+'@gravitational/design-system': patch
+---
+
+this is a test changeset to test publishing

.github/workflows/bot.yml

@@ -0,0 +1,49 @@
+name: Changeset Bot
+
+on:
+  pull_request:
+    types: [opened, synchronize, reopened]
+
+permissions:
+  contents: read
+  pull-requests: write
+  issues: write
+
+env:
+  NODE_VERSION: 22.x
+
+jobs:
+  changeset-bot:
+    name: Changeset Bot
+    runs-on: ubuntu-latest
+    if: ${{ !startsWith(github.event.pull_request.head.ref, 'changeset-release') }}
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v5
+        with:
+          fetch-depth: 0
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: ${{ env.NODE_VERSION }}
+
+      - name: Enable Corepack
+        run: corepack enable
+
+      - name: Install dependencies
+        run: pnpm install --frozen-lockfile
+
+      - name: Install bot dependencies
+        run: pnpm install --frozen-lockfile
+        working-directory: bot
+
+      - name: Run changeset bot
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          pnpm bot \
+            ${{ github.repository_owner }} \
+            ${{ github.event.repository.name }} \
+            ${{ github.event.pull_request.number }} \
+            ${{ github.event.action }}

bot/getChangedPackages.ts

@@ -0,0 +1,155 @@
+import assembleReleasePlan from '@changesets/assemble-release-plan';
+import { parse as parseConfig } from '@changesets/config';
+import parseChangeset from '@changesets/parse';
+import type {
+  NewChangeset,
+  PackageJSON,
+  PreState,
+  WrittenConfig,
+} from '@changesets/types';
+import type { Package, Packages } from '@manypkg/get-packages';
+import type { Octokit } from '@octokit/rest';
+import fetch from 'node-fetch';
+
+export async function getChangedPackages({
+  owner,
+  repo,
+  ref,
+  changedFiles: changedFilesPromise,
+  octokit,
+}: {
+  owner: string;
+  repo: string;
+  ref: string;
+  changedFiles: string[] | Promise<string[]>;
+  octokit: InstanceType<typeof Octokit>;
+}) {
+  let hasErrored = false;
+
+  const githubToken = process.env.GITHUB_TOKEN;
+
+  function fetchFile(path: string) {
+    return fetch(
+      `https://raw.githubusercontent.com/${owner}/${repo}/${ref}/${path}`,
+      {
+        headers: {
+          Authorization: `Bearer ${githubToken}`,
+        },
+      }
+    );
+  }
+
+  async function fetchJsonFile<T>(path: string): Promise<T> {
+    try {
+      const x = await fetchFile(path);
+
+      return (await x.json()) as T;
+    } catch (err) {
+      hasErrored = true;
+
+      // eslint-disable-next-line no-console
+      console.error(err);
+
+      return {} as T;
+    }
+  }
+
+  async function fetchTextFile(path: string) {
+    try {
+      const x = await fetchFile(path);
+
+      return await x.text();
+    } catch (err) {
+      hasErrored = true;
+
+      // eslint-disable-next-line no-console
+      console.error(err);
+
+      return '';
+    }
+  }
+
+  const rootPackageJsonContentsPromise =
+    fetchJsonFile<PackageJSON>('package.json');
+  const configPromise: Promise<WrittenConfig> = fetchJsonFile(
+    '.changeset/config.json'
+  );
+
+  const tree = await octokit.rest.git.getTree({
+    owner,
+    repo,
+    recursive: '1',
+    tree_sha: ref,
+  });
+
+  const changedFiles = await changedFilesPromise;
+
+  let preStatePromise: Promise<PreState> | undefined;
+  let changesetPromises: Promise<NewChangeset>[] = [];
+
+  for (let item of tree.data.tree) {
+    if (!item.path) {
+      continue;
+    }
+
+    if (item.path === '.changeset/pre.json') {
+      preStatePromise = fetchJsonFile('.changeset/pre.json');
+
+      continue;
+    }
+
+    if (
+      item.path !== '.changeset/README.md' &&
+      item.path.startsWith('.changeset') &&
+      item.path.endsWith('.md') &&
+      changedFiles.includes(item.path)
+    ) {
+      const res = /\.changeset\/([^.]+)\.md/.exec(item.path);
+      if (!res) {
+        throw new Error('could not get name from changeset filename');
+      }
+
+      const id = res[1];
+
+      changesetPromises.push(
+        fetchTextFile(item.path).then(text => {
+          return { ...parseChangeset(text), id };
+        })
+      );
+    }
+  }
+
+  let rootPackageJsonContent = await rootPackageJsonContentsPromise;
+
+  // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
+  if (hasErrored) {
+    throw new Error('an error occurred when fetching files');
+  }
+
+  const root: Package = {
+    dir: '.',
+    packageJson: rootPackageJsonContent,
+  };
+
+  const packages: Packages = {
+    root,
+    tool: 'pnpm',
+    packages: [root],
+  };
+
+  const releasePlan = assembleReleasePlan(
+    await Promise.all(changesetPromises),
+    packages,
+    await configPromise.then(rawConfig => parseConfig(rawConfig, packages)),
+    await preStatePromise
+  );
+
+  return {
+    changedPackages: packages.packages
+      .filter(pkg =>
+        changedFiles.some(changedFile => changedFile.startsWith(`${pkg.dir}/`))
+      )
+      .map(x => x.packageJson.name),
+    releasePlan,
+  };
+}